We propose to study the mechanisms of potential production in the photoreceptors and the distal interneurons of the vertebrate retina and the insect compound eye using primarily electrophysiological techniques. The mechanism of phototransduction will be investigated using photoreceptor mutants of Drosophila. The ionic and synaptic mechanisms will be studied on the horizontal and bipolar cells of the vertebrate retina. Attempts will be made to gain insight into the organization of the retinal circuitry. BIBLIOGRAPHIC REFERENCES: Waloga, G., and W.L. Pak. 1976. Horizontal cell potentials: dependence on external sodium ion concentration. Science 191:964-966. Grabowski, S.R., and W.L. Pak. 1976. Fast electrical responses from Drosophila metarhodopsin. Abstr., Assoc. Res. Vision Ophthalmol. p. 16, #3.